A lot of important decisions are made in the context of social interactions because we live in highly complex social environments. In order to investigate social decision-making in the laboratory setting, simple but sophisticated tasks such as Ultimatum game, Prisoner’s dilemma, and Trust game have been used from a branch of behavioral economics. Recently, a variety of neuroscience methods including functional neuroimaging, brain-damaged neurological patients, transcranial magnetic stimulation, pharmacological manipulations have been used to examine the underlying neural networks for social decision making. Neural systems such as insula, caudate nucleus, ventromedial, ventrolateral, dorsolateral, and dorsomedial prefrontal cortex are recruited for inequity aversion, reciprocity, abstract and delayed reward, emotional regulation, social norm, and mentalizing respectively. These neural systems are also modulated by neurochemicals including serotonin and testosterone, which promote and suppress prosocial behavior respectively. Additionally, recent progress has been made in understanding the neural differences between normal subjects and patients with mental illness in social decision-making. Overall, the study of social decision-making in the perspective of neurobiology has been growing rapidly and the current state of knowledge as described here seems to provide many interesting avenues for future research.